Police continue extensive anti-terrorism raids today after arresting four men for an alleged terror plot on Saturday night in Sydney.
The men, who were arrested after raids in Lakemba, Surry Hills, Punchbowl and Wiley Park, have been accused of plotting a terrorist attack on a plane.
Investigators said items were found at the Surry Hills home that could have been used to make a homemade bomb which is understood to be “ready to go”.
Until the arrests, the men, who are father and sons linked by marriage, were unknown to authorities bar one conviction for negligent driving between them.
However, police say they picked up a “small piece of intelligence” about the intent to use a crude homemade bomb on a passenger plane they would detonate mid-flight and arrested the men after surveillance, deeming them too much of a threat to public safety.
“You need to make the decision at some stage, when is the right time to go. Both [Australian Federal Police] and NSW Police agreed last night was the right time to go,” NSW Police Commissioner Mick Fuller said on Sunday.
Unlike other crimes, the men could be held for days before knowing the specific allegations against them, with authorities reviewing their detention every 12 hours for up to seven days.
This will give police time to gather a substantial amount of evidence to bring a potential case against the group.
"The reality is, with terrorism, you can't wait, you can't wait until you put the whole puzzle together," Mr Fuller said.
"You do have to go early because if you get it wrong, the consequences are severe."
Security at airports was immediately increased by Prime Minister Malcolm Turnbull who said the raids “disrupted” what appeared to be an “elaborate” conspiracy.
"Some of the measures will be obvious to the country, some will not be," he said. "Travellers should be prepared for additional scrutiny at screening points."
WATCH: Two homeless men describe how they helped after Manchester terror attack.
Turnbull warned travellers to arrive at terminals at least two hours before flights, limit carry on and check baggage and to ensure they check with airlines for further advice on the extent on the effect of the measures.
Meanwhile, an aviation security expert has warned the majority of airport workers across Australia have not been given the appropriate training to effectively handle a terrorist attack.
Speaking to ABC Dr John Coyne, head of border security at the Australian Strategic Policy Institute, explained how tricky it was anticipating new ways terrorists could attack airlines.
While banning carry-on all together had been discussed in the wake of 9/11, he doesn’t believe restriction is the answer.
"I think improving search capability and improving search process — so improving x-ray machines, swipes for explosive residue," he said.
"It is about making sure intelligence information is linked to those responsible for physical security, the operators.
"They've got to get lucky once - you've got to be lucky all the time."